Binary Counter using verilog

A binary counter is a simple counter that has an initial value of 0 at the time of reset. It value keeps incrementing by 1 at each clock cycle. And finally it reaches its maximum value, say 1111 in binary for a 4 bit counter, it again reaches 0000 in binary and keeps counting one.

Here is the verilog implemmentation of shift register. 


  1. // referencedesigner.com
  2. // Example of binary_counter
  3. module binary_counter
  4.    #(parameter N=4)
  5.    (
  6.     input wire clk, reset,
  7.     output wire [N-1:0] binary
  8.    );
  9.  
  10.    reg [N-1:0] r_reg;
  11.    wire [N-1:0] r_next;
  12.  
  13.    always @(posedge clk, negedge reset)
  14.    begin
  15.       if (~reset)
  16.          r_reg <= 0;
  17.       else
  18.          r_reg <= r_next;
  19. 	end	
  20. 	assign binary  = r_reg;
  21. 	assign r_next = r_reg+1;
  22. endmodule


Explanation

We make use of the simple addition statement for incrementing value. We should note the property of addition that - it wraps when it reaches its max value. 

assign r_next = r_reg+1;;




The testbech for the binary counter 

  1. `timescale 1ns / 1ps
  2. module stimulus;
  3. 	// Inputs
  4. 	reg clk ;
  5. 	reg reset;
  6. 	// Output
  7. 	wire[3:0] binary;
  8. 	// Instantiate the Binary Counter
  9. 	binary_counter  #(4) s1  (
  10. 		.clk(clk), 
  11. 		.reset(reset),
  12. 		.binary(binary)
  13. 	);
  14.  
  15.  integer i;
  16.  initial 
  17.  begin
  18.  
  19.  clk = 0;
  20.  for(i =0; i<=40; i=i+1)
  21.  begin
  22.   #10 clk = ~clk;
  23.  end
  24.  end
  25.  
  26. initial 
  27. begin
  28.  
  29. $dumpfile("test.vcd");
  30. $dumpvars(0,stimulus);
  31.  
  32. reset =1;
  33. #2 reset = 0;
  34. #2 reset =1;
  35. end
  36.  
  37.  
  38. 		initial begin
  39. 		 $monitor("clk=%d binary=%4b",clk,binary);
  40. 		 end
  41.  
  42. endmodule


Exercise

1. Change the binary counter so that it counts down in place of count up

- Answer here

2. Modify the code so that, it gives output 1 ( define another output wire), for one clock period every time it reaches max value.

Answer here

and test bench here

2. Modify the code so that, it has another input, call it load. When it is 1, at the next rising edge of clock, the counter value is uploaded with N bit wide input - call it input_load. It then keeps counting from there.